Melitracene

Haloperidol is a neuroleptic drug. Haloperidol is used to treat acute or chronic schizophrenia, tics in Tourette's syndrome, mania in bipolar disorder, nausea and vomiting, delirium, agitation, acute psychosis, and hallucinations in alcohol withdrawal. It can be administered by mouth or by injection. Haloperidol is available by prescription only.

Pharmacodynamics

While haloperidol exhibits pharmacological activity at a number of receptors in the brain, it exerts its antipsychotic effects through its potent antagonism of the dopamine receptor (mainly D2), particularly in the mesolimbic and mesocortical systems of the brain. It also binds to α1-receptors and, at higher doses, to 5-HT2-receptors.

Pharmacokinetics

Haloperidol is a highly lipophilic compound and is highly metabolized in humans, which may cause wide interindividual variability in its pharmacokinetics. Haloperidol is well absorbed from the gastrointestinal tract when taken orally, but the first-pass effect reduces oral bioavailability to 40-75%. Enzymes involved in the biotransformation of haloperidol include CYP3A4 and CYP2D6 and carbonyl reductase. Plasma protein binding is only about 10%. After oral administration, the half-life is approximately 14.5-36.7 hours. After intramuscular injection, the mean half-life is 20.7 hours. Haloperidol and its metabolites are almost entirely excreted in the urine.

Drug Interactions

Interactions, some of which may be threatening, may occur with the following drugs:

• Amiodarone: QT interval prolongation.
• levodopa: reduced effect of levodopa
• Lithium
• Methyldopa: increased risk of extrapyramidal side effects and other adverse central effects
• Other centrally depressant drugs (alcohol, tranquilizers, narcotics): effects and side effects of these drugs (sedation, respiratory depression) are increased. In particular, doses of concomitant opioids may be reduced by 50% for chronic pain.
• Other drugs metabolized by the CYP3A4 enzyme system: Inducers such as carbamazepine, phenobarbital and rifampicin decrease plasma levels and inhibitors such as quinidine and fluoxetine increase plasma levels.
  Trizyklische Antidepressiva: Metabolismus und Elimination von Trizyklika signifikant vermindert, erhöhte Toxizität festgestellt (anticholinerge und kardiovaskuläre Nebenwirkungen, Absenkung der Krampfschwelle

Side effects:

Common side effects:

Extrapyramidal side effects including:

• Akathisia (motor restlessness).
• dystonia (persistent spasms and muscle contractions)
• Muscle rigidity
• Parkinsonism (characteristic symptoms such as rigidity)
• hypotension (drop in blood pressure)

Anticholinergic side effects such as:

• blurred vision
• Constipation
• dry mouth
• Somnolence

Toxicological data:

LD50 (rat, oral): 128 mg-kg-1